Sensitizer containing a gel-forming



Reisaued Dec. 19, 1944 I SENSITIZER CONTAINING A GEL-FORMING COLLOIDALCLAY Clyde A. Crowley, Chicago, and John B. Mullen, Elgin, Ill.,assignors to The Huey 00., Chicago, Ill., a corporation of Illinois NoDrawing. Original No. 2,317,521, dated April 27, 1943, Serial No.416,046, October 22, 1941. Application for reissue September 18, 1944,Se-

rial No. 554,599%

9 Claims.

This invention relates to improvements in the sensitized layers ofphotosensitive papers, and to means of accomplishing these improvements.An object of this invention is the formation of advantages generallyfound in processes in which an aqueous sensitizing solution is appliedto paper or similar base, and arising largely from penetration of thesensitizer into the paper, can

sensitized layers with improved properties, parbe summarized briefly asfollows: ticularly sensitized layers which have higher (1) The speed isreduced by penetration; (2) printing speed, which can be washed morerapidthe ease, speed, and completeness of washing ly, and which willgive images of greater sharpare lowered; and (3) the possibility ofbleeding ness, better definition, and improved clarity. and ofindistinct lines is increased. All or some The types of sensitizers towhich our invention of these iflle lties are found in l epri p pers. isapplied are so-called "b1ueprint .sensitizers, whether of the ordinary ew type either of the negative or direct positive type; Containingfel'rieyanide, e yp diazo sensitizers; and direct line iron sensitizers,containing ferrocyanide; in diazo papers; and in In general, ourinvention can be used with any the Various direct line iron p p suchtype of sensitized layer which is applied to Va means have been triedeliminate a base bi paper, cloth, or the equivalent from these troubles.By increasing the concentration solution in water, whatever the activelight sen- 0f the sensitizel. it is Possible to increase its sitivechemicals thereof may be. viscosity and, therefore, to reducepenetration. In the ordinary process of preparing blueprin However, thismethod causes great diiiiculty in papers, paper or other suitable baseis coated the coating P since the h y concentrated with a solution whichcomprises light-sensitive solutions e subjecttocrystalliz ion e slferric compounds such as ammonium ferri-oxaevap r ion C e in temperatureOccurs, and late, a ferricyanide salt, and usually so-called will, thre. n e in composition (affectin "solubilizing or buffering agents suchas potasthe nature of the sensitized layer), and may even slum oxalate,which are used primarily to imdepos t c y t 0 t e Paper The use Of aprove the keeping and washing quality of the hard-surfaced paper hasalso been tried, which sensitized paper. The customary practice is toreduces Penetration and actually makes it P pass the paper stock overcoatin rollers, which sible to eliminate the 85 in pe and s ow apply thesensitizing solution, after which the of washing caused by pe t t o e inpaper is dried. It is common practic'e to apply practice it is not Po eo use a p p W a two coats of the sensitizin solution beforedrysumciently hard-sized, non-absorbent surfaceto ing. The papers aresubsequently exposed to eliminate these eflects entirely, since to do solightunder a design, washed to remove unreacted would mean that thesensitized a r o the P pe chemicals, developed in a solution of anoxidizing would be so thin t t it would give gro agent such as potassiumdichromate, and rinsed ffi i nt pi m n ion Al since w p ner beforedrying. The resulting prints arev negaof this type of surface there isno means 01' bondtives of the original design, with white lines onsensitizing chemicals o e e and a blue background. they are actuallylaid on the surface, bleeding is This process suffers from a number ofdisadactually increased rat e t e vantages. In the first place, thesensitizer penedo some means tt g the sensitized layer trates into thepaper below the surface for a firmly t0 e P p s required. and no betterconsiderable distance. This has two undesirable method for use w th aquus s uti n s nsitizers efl'ects: first, it slows down the action of liht has been found then ati n int h pap r. on the sensitive chemicalsappreciably, since these The best that has been done o date i to at mpchemicals are partially conc d i th paper to control the penetration bymeans of the surface matrix; and secondly, for the same reason, it Sizeon the P makes washing slower than is desirable and often We havediscovered met od whereby aqueless thorough. In addition, partiallybecause ous solution sensitizers of the types described washing must beprotracted, some chemicals may above in aqueOlls Solution can be app toP p wash or bleed from th exposed t th or similar base, which eliminatesin whole or in exposed areas, causing indistinct lines and part theseobjectionable features found hitherto. images. The contrast is alsoreduced thereby. Our invention consists in the use of a sensitiz- Inother types of sensitive papers of the gening solution which containsbentonite or an era] type described above, the same difficultiesequivalent p f gel-forming colloidal clay. occur also in greater or lessdegree. The dis- M whi h is coated onto the paper or other base. By

the use of such a sensitizer, it is possible. to

obtain a sensitized coating which is substantially on the surface of thepaper, so that it is in a position to react most rapidly with the light;soluble unreacted chemicals can be washed out more readily andcompletely, and as the bentonite (or its'e'quivalent) serves to bind thechemicals to the paper, reaction products are less likely to be washedinto the unexposed areas.

In the practice of this invention, an aqueous sensitizing solution orsuspension containing the light-sensitive chemicals and bentonite isap-.

plied to the surface of the paper, cloth or other base by any suitablemeans. One method of application is the use of coating rollers similarto those ordinarily used with aqueous sensitizers;

by adJusting the tension on the paper as it passes over the coatingrollers, it is possible to lay down a satisfactory film, which issmoothed, and excess material removed, if necessary, by use of asqueegee rod or a doctor's knife. Other methods of application can alsobe used, and will readily oi bentonite, our invention is not limited tothis explanation.

Example I A. Bentonite 10 Water ml 96 B. Ammonium oxalate g.. 6

Citric a I I 6. Ferric ammonium oxalate g 39 Potassium ferricyanide gWater to make ..ml 244 I (Density 13 B.)

The B solution is added to the bentonite suspension A while stirring.The paper sensitized with this solution is exposed under a design tolight, washed, developed with an oxidizing agent,

- and again washed. Paper coated with this sensisuggest themselves-tothose skilled in the art;

. and our invention is not limited to any method of applicat on of thesensitized layer.

The amount of bentonite required varies with the nature of the paper orother base and with the nature of the sensitizing solution. The'quantityof bentonite should be sufilcient to increase the viscosity of thesensitizer," and to prevent substantially all penetration into thepaper.

tizer is faster and washes better giving clearer prints than papersensitized with a sensitizer identical in composition except for theomission of the bentonite.

Example II A. Bentonite ...g 16.00 Water e ml 145.00 B. Oxaiic acid(HzCzOiBHzO) g 6.00 Potassium, carbonate (K130321120) g 13.31 Potassiumferrocyanide ..g 15.00 Potassium ferricyanide ..-g 0.375 Ferric ammoniumoxalate g 30.00

. Water to make --.ml j 314 (Density 13.2" B.)

Solution B is added to the bentonite dispersion A while stirring. Thepaper sensitized with this solution is exposed under a design to light,washed to remove excess or unreacted chemicals, treated with anoxidizing agent, washed again. and dried.

use a relatively hard-surfaced paper which has a low tendency to absorbwater. Such a paper can be prepared by use ofa glue size which .issubsequently tannedby-formaldehyde or other agents, by sizing withresins such as urea-dormaldehyde type, by use of other types of surfacesizes, or by super calendering, or by combinations of these means or byother means. However, it is possible by proper control of the sensitizerto obtain good results even on papers of more open or porous structure,and our invention is not limited to any particular type of paper.

.We have mentioned the fact that bentonite increases the viscosity ofthe-sensitizer; however, this is not believed to be the sole explanationof its eflect in reducing penetration into the paper. If: such were thecase, its-.wo'uld be possible simply by increasing the content ofdissolved solids, for example by the addition of sugar, to increase theviscosity sufliciently to reduce penetration. However, although this hasbeen attempted in the past, it is possible to achieve the eiiect desiredonly to a limited extent by this method. vBentonite and other geliormingcolloidal clays are hydrophilic colloids, and when dispersed in waterthey reduce the amount of free or available water. By so' doingbentonite increases the viscosity of the solu-, tion, but its effectsare not ascribable to the increased viscosity alone, but rather to thereduction in the free water, since all or a large part of the water islinked to the bentonite (or to the ions) as water by hydration. Whilethis. is believed to be the true explanation of the action The paper sosensitized gives higherprinting speed, easier washing and sharper printsthan paper prepared with the same sensitizer with bentonite omitted.

Erample m a A diazo sensitizer is prepared as follows:

A. Diazo sensitizer g 70.0 B. Bentonite, g 3.0

Water A is added to B and mixed thoroughly. The

- mixture .is coated on to paper, and the Paper is exposed under adesign to light. Development is eilected with an alkaline solution of acoupling agent consisting of 'phloro-glucinol, resorcinol, sodiumcarbonate, and water.

Diazo papers can also be prepared under this invention by incorporatingin the sensitizer the coupling compounds; the sensitizer must then beacidto prevent coupling. Such papers are developed after exposure bytreatment with a solution of an alkali or by exposure to a moistatmosphere containing ammonia or other alkaline The term "bentonite" isintended to describe the .colloidal clay found almost exclusively inWyoming. The term is not a trade name, but a generic name descriptive ofthe clay found in the Fort Benton area. There are other si ar colloidalclays found in other parts of the United States and known assubbentonite clays and available for use, although with lesseffectiveness in the use outlined inthe foregoing description.

It will be understood that this invention is not restricted to theparticular sensitizers shown which are cited merely as examples of thetype with which our invention is concerned; and no -ite andlight-sensitive chemicals selected from the group consisting of 1)blueprint sensitizers. (2) diazo sensitizers, and (3) direct line ironsensitizers.

4. A sensitizer comprising gel-forming bentonite and an aqueous solutionof light-sensitive chemicals selected from the group consisting of (1)blueprint sensitizers, (2) diazo sensitizers and (3) direct line ironsensitizers.

5. A sheet containing a layer of gel-forming bentonite andlight-sensitive chemicals selected from the group consisting of (1)blueprint sensi- I tizers, (2) diazo sensitizers and (3) direct lineiron sensitizers,

v gel-forming bentonite and light-sensitive chemicals selected from thegroup consisting of (1) blueprint sensitizers. (2) diazo sensitizers and(3) direct line iron sensitizers, said bentonite acting r to inhibitpenetration of the sensitizer into the body of the sheet.

7. A sheet having a composite layer including gel-forming bentonite andlight-sensitive chemicals, said gel-forming bentonite acting to inhibitpenetration of the light-sensitive chemicals into the body of the sheet,said gel-forming bentonite being present in the proportion of 1 to 10%by weight of the light-sensitive chemicals, said lightsensitivechemicals being selected from the group consisting of (1) blueprintsensitizers, (2) diazo sensitizers and (3) direct line iron sensitizers.

8. A sensitizer for blueprint paper including a light-sensitive ferriccompound and a minor proportion of a gel-forming colloidal clay.

9. Blueprint paper comprising-a sheethaving a composite layer includinga sensitizer comprising light-sensitive ferric compound and a minorproportion of a gel-forming colloidal'clay, said clay acting to inhibitpenetration of the sensitizer chemicals into the body of the sheet.

CLYDE A. CROWLEY.

JOHN B. MULLER.

